This is a Clojure program designed to realistically replay HTTP GET requests from a log file to the server of your choice. By "realistically", I mean it does its best to ensure that requests are made in the order they originally arrived, and at a similar rate.

Why another load testing tool? I had trouble finding something that could take an existing log file and generate similar traffic patterns based off its timestamps, and I wanted something that didn't rely on a whole bunch of threads for concurrency (this tool uses NIO to fire many requests from a single thread).

Building it

The usual steps:

1. Get Leiningen from http://github.com/technomancy/leiningen and put the 'lein' script somewhere in your $PATH.

2. Run 'lein uberjar'. Lein will grab all required dependencies and produce a 'traffic-replayer-[VERSION].jar'.

Using it

Using this program is a two step process: you generate a script file (containing URLs requested and timing information), and then you replay it at a specified host.

Generating a script file

You could do this yourself using Perl/sed/awk/whatever, but this program does know how to generate script files from HAProxy logs. The script file format is just:

[ms since epoch]\t[requested URI (e.g. /foo)]

Lines must be sorted numerically by the timestamp (e.g. sort -n -k1).

To generate a script file from a HAProxy log, I used:

$ grep 'GET /some/url' ~/some.log.2010-07-19 | \
    java -jar traffic-replayer-[VERSION].jar generate /dev/stdin script.out

HaProxy logs work well because they log the time the request was received, as well as the time it completed (many servers only log the latter, which is less useful for this sort of thing).

Replaying a script file

Replay a script file is similar:

# To replay traffic against http://localhost/someprefix
#
$ java -jar traffic-replayer-[VERSION].jar replay script.out http://localhost/someprefix run.log

On the console you'll see timing information ("sleeping NNN ms before next request"). In your run.log you'll see each URL that has been requested and how long it took to come back.